Project Title: Tropospheric Scintillations

Project Description:

The phase of radio waves propagating through the earth's troposphere is perturbed by irregularities in the refractive index. At microwave frequencies, these perturbations are dominated by water vapor fluctuations. Phase perturbations are important because they affect the "seeing conditions" of imaging radio interferometers and because, if uncalibrated, they may be the limiting noise source in future searches for low-frequency gravitational radiation using Doppler tracking of spacecraft.

This project involves the measurement of statistics of tropospheric scintillations observed using using very-high-precision spacecraft tracking data and, as appropriate, a cross-spectral analysis of radio phase fluctuations with water vapor radiometer (WVR) data taken simultaneously. In addition to second-moment statistics (power spectra, structure functions), the magnitude and frequency of occurrence of non-stationary tropospheric "events" are also of interest.

Background Information:

The data were taken at three sites (California, Spain, Australia) nearly continuously for 19 days and over a wide range of tropospheric conditions. The data were "X-band" (~8.4 GHz), so the effect of phase perturbations imposed by charged particles (e.g. the ionosphere) were minimized. The data have been reduced to phase residuals. The phase residuals have to be inspected and partitioned into regions that are approximately statistically stationary and into regions of non-statistical events. Spectral, cross-spectral, and structure function analysis will be done, building the required programs from an existing subroutine library.

Literature References:

On the relevance of phase scintillation to the low-frequency gravitational wave search problem: Armstrong, J. W., Woo, R., and Estabrook, F. B. 1979, Ap. J. 230, 580.

Existing observations of tropospheric phase fluctuations, e.g.: Armstrong, J. W. and Sramek, R. A. 1982, Radio Science, 17, 1579; Sramek, R. A. 1989, in "Radio Astronomical Seeing", J. E. Baldwin and Wang Szhouguan, eds. (Pergamon: Oxford)

A general review of wave propagation in a random medium: Ishimaru, A, "Wave Propagation and Scattering in Random Media" (Academic Press: New York)

Requirements:

The sponsor requires that interested students meet the following requirements: Junior or senior level standing with course work and interest in applied mathematics (particularly numerical analysis and linear algebra); possibly a mathematics major with some exposure to computer science. Familiarity with FORTRAN, some exposure to probability and its applications, and some exposure to a UNIX environment are required.

This opportunity is for:

Caltech students. Will consider non-Caltech students

Research Sponsor

Sponsor: John Armstrong
Division: JPL
Mail Code: 238-737
Phone: (818) 354-3151
E-mail: john@oberon.jpl.nasa.gov